Low loss glass-ceramic materials, method of making same and electronic packages including same

ABSTRACT

A glass-ceramic is provided having a thermal expansion coefficient in a range of 3-6 ppm/° C., a dielectric constant that is less than 5 and a Quality factor Q of at least 400. The glass-ceramic consists essentially of SiO 2  in a range of 45-58 wt %, Al 2 O 3  in a range of 10-18 wt % and MgO in a range of 10-25 wt %. A method of making the glass-ceramic is also provided. Further, an electronic package is also provided, including a base member and a glass-ceramic substrate bonded to the base member.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.11/084,722, filed Mar. 18, 2005, now issued, and also claims the benefitof U.S. Provisional Application Ser. No. 60/585,689 filed Jul. 6, 2004,the entireties of which are incorporated herein by reference.

This application is related to copending U.S. Pat. No. 7,186,461(Attorney Docket No. 851_(—)019 NP), issued Mar. 6, 2007, entitled‘GLASS-CERAMIC MATERIALS AND ELECTRONIC PACKAGES INCLUDING SAME,” whichclaims the benefit of U.S. Provisional Application Ser. No. 60/574,828filed May 27, 2004 and U.S. Provisional Application Ser. No. 60/585,743filed Jul. 6, 2004, the entireties of which are incorporated herein byreference.

FIELD OF THE INVENTION

The present invention relates to glass-ceramic materials for use in highfrequency (i.e., gigahertz range) electronic applications, a method ofmaking a glass-ceramic substrate and various ceramic packagingassemblies including glass-ceramic materials for use in high frequencyelectronic applications.

BACKGROUND OF THE INVENTION

Known multi-layered ceramic circuit boards are typically fabricated byforming layered stacks of ceramic dielectric tape, which are typicallyknown as green tapes or green sheets. The green tapes typically comprisea ceramic material powder and/or glass powder that is mixed withsuitable organic binders or resins, solvents, plasticizers andsurfactants and formed into a tape. The process for making high densitymulti-layer circuit boards typically involves forming a plurality ofpre-fabricated green tape layers having via holes punched therein,applying or printing circuit patterns on the layers using a conductiveink, i.e., a mixture of a conductive metal powder and a non-metallicpowder including a glass and/or a ceramic in a solvent/binder mixture,filling the vias with the conductive ink so that the various circuitlayers can be connected to one another through the thickness of thecircuit board, and laminating the green tape layers together by pressingthe layers into a stack. The stacked layers are then fired at atemperature exceeding 700° C. to burn off organic materials and todensify the green tape material to form a sintered glass and/or ceramic.

The sintered glass and/or ceramic circuit boards are typically quitefragile, however, and in order to impart additional mechanical strengthto the laminated board, the circuit boards are often attached to one orboth sides of a suitable support substrate, or core material. Inaddition, it may be desired to mount active, heat generating devicessuch as integrated circuits onto a high thermal conductivity member madeof a metal or certain ceramics (e.g., AlN, SiC, etc.). In suchsituations, the glass and/or ceramic substrates are typically joined tothe support structure via a solder-type bonding procedure, which isperformed at low temperatures that are much less than the sinteringtemperature of the glass and/or ceramic substrate. Hereinafter,applications involving sintered substrates that are subsequently joinedto a support core or other member are referred to as non-co-firedapplications.

It is also possible to join a green laminated structure with a supportmember or other component as the green laminate is sintered. That is,the green laminated structure is first adhered to a support member andthe structure is then fired to a temperature that is sufficient to (1)remove the organic materials from the green tapes and the conductiveinks, (2) sinter or densify the particles of the green tape compositionand the metal particles of the conductive inks to form a sinteredmulti-layer ceramic and/or glass body, and (3) sufficiently adhere thesintered multi-layer body to the support substrate. Hereinafter,applications involving green laminated structures that are fired with asupport core are referred to as co-firing applications.

In both co-fired and non-co-fired cases, once bonding and densificationhave occurred, it is important that the sintered multi-layer body andthe cooperating support structure have reasonably compatible thermalexpansion characteristics, preferably closely matched thermal expansioncoefficients. In most cases, however, the thermal expansion coefficient(hereinafter TEC) of the glass and/or ceramic laminate material does notclosely match that of the support substrate or core on which thelaminates are provided.

This thermal expansion mismatch problem is an important issue with lowtemperature co-fired ceramics (herein after LTCC) that are known inceramic packaging applications, where a green laminated structure issintered at a relatively low temperature after first being adhered tothe metal support core. For example, densification of the greenlaminated structures during sintering can produce a large degree ofvolume shrinkage in the ceramic and/or glass material, for example, upto about 35-55 percent by volume. If the green laminated body iseffectively bonded to an already dense support substrate or core (i.e.,a core that does not itself shrink during the sintering process), thegreen laminated body will be constrained from sintering in the plane ofthe support substrate/core, which itself does not typically experiencedensification shrinkage when subjected to the typical sinteringtemperatures. This can create stresses that can be accentuated by thedifferent expansion behaviors of the glass and/or ceramic substrate andthe support member, both during the bonding process and in subsequentuse in a thermally active environment.

The difference between the TEC of the material of the multi-layersubstrate and that of the support substrate or core can, indeed, lead tosubstantial problems. For example, significant stresses can develop,particularly at the bonding interface, that lead to warping or othermechanical damage, such as non-adherence to the support substrate andmisalignment between vias that are provided in the multi-layered bodyand the corresponding electrical feed-throughs provided on the supportsubstrate or core. In severe cases, it is possible that the multi-layersubstrate will even separate from the support, thus rendering the deviceunacceptable for use.

For example, most conventional, commercially available LTCC tapes have aTEC on the order of 6 to 8 ppm/° C. This often does not closely matchthe TEC of commonly used metal support cores, including laminatedCopper-Molybdenum-Copper support cores and KOVAR® support cores. Forexample, a typical laminated Cu/Mo/Cu (13/74/13) support core has a TECfrom room temperature to 300° C. (hereinafter α_(RT-300)) of about 5.3ppm/° C. and, when plated with Ni, the laminated Cu/Mo/Cu (13/74/13)support core has an α_(RT-300) of about 5.75 ppm/° C. For KOVAR®, theα_(RT-300) is about 5 ppm/° C.

It is also important that the TEC of the sintered multi-layer glassand/or ceramic substrate closely matches that of the structure to whichit is bonded in non-co-firing applications, as well as in stand-alonesubstrate applications, where the multi-layer glass and/or ceramicsubstrate is bonded to, or installed in connection with, another memberor device, as mentioned above. That is, is desirable to prevent thermaland mechanical stresses from arising when the final structure is used inthe intended applications, which typically include temperature cyclingenvironments.

For the reasons explained above, it would be desirable to provide amaterial for a multi-layer substrate that has a TEC that closelymatches, or that can otherwise be easily tailored to match, that of theintended support core or base member to which the multi-layer substrateis to be joined or otherwise installed.

Most ceramic and glass materials that have a suitable TEC, however, donot also have a suitably low dielectric constant (K) and low losstangent (or high Q factor), which makes these ceramic materials lessdesirable for high frequency electronic applications. Along those lines,most ceramic and glass materials having a suitably low dielectricconstant and high Q factor do not have a suitable TEC, and inparticular, the TEC often cannot be tailored to achieve a closer matchto that of the base structure to which the multi-layer substrate is tobe bonded.

It would be more desirable, therefore, to provide a multi-layersubstrate material that has a desirable TEC along with desirableelectrical properties, such as a very low dielectric constant (K) and ahigh Q factor, that is, 1/loss tangent.

In addition, it would also be desirable to provide a material for amulti-layer substrate that is sufficiently densified at relatively lowsintering temperatures, e.g., at temperatures less than 950° C., andthat can be suitably provided with, and co-fired with, relatively lowmelting-point, low resistance metals, such as Ag, Cu and such alloys,especially for LTCC-type applications. Most ceramic and some glass orglass-based materials, however, require significant heat-treatment attemperatures exceeding 950° C. in order to achieve sufficientdensification and the desired electrical characteristics. When higherprocessing temperatures are involved, however, metals having a highermelting-point need to be used, especially for electronic applicationsthat involve high frequencies (i.e., up to 60 GHz).

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a glass-ceramic thatis suitable for use as a multi-layer substrate in high frequencyelectronic packaging applications such as low temperature co-firedceramic (LTCC) applications, co-fired ceramic on metal applications(i.e., a metal-ceramic substrate with wiring and attached active andpassive circuit elements) and thin-film metallized glass-ceramicpackages bonded to assemblies or substrates made of ceramic or metal,for example. It is also an object of the present invention to provide anelectronic packaging assembly including such glass-ceramics.Additionally, it is an object of the present invention to provide aglass-ceramic material that is suitable for stand-alone substrateapplications, such as a substrate with thin-film wiring, for use in highfrequency electronic applications.

The glass-ceramic material according to the present invention has athermal expansion coefficient in a range of 3-6 ppm/° C. This TEC rangeeither closely matches, or can easily be tailored to better match, thatof the desired support core or base material to which the multi-layerceramic substrate is to be joined. The glass-ceramic material accordingto some embodiments of the present invention are sufficiently densifiedwhen sintered to a relatively low temperature of about 900-950° C., havea low dielectric constant of less than 5, preferably less than 4.75, andalso has a very low loss tangent (i.e., a high Q factor of greater than400, more preferably, greater than 500, and even more preferably,greater than 550).

When fired at higher sintering temperatures, and in some cases, with theaddition of a high TEC additive such as quartz, the glass-ceramicmaterial according to some embodiments of the present invention exhibitsa very high Q, low K, and a slightly higher TEC in a range of 4-6 ppm/°C.

According to one embodiment of the present invention, a glass-ceramic isprovided having a thermal expansion coefficient in a range of 3-6 ppm/°C., a dielectric constant in a range of less than 5 and a Quality factorQ of at least 400. The glass-ceramic of the present invention consistsessentially of SiO₂ in a range of 45-58 wt %, Al₂O₃ in a range of 10-18wt % and MgO in a range of 10-25 wt %. SiO₂, Al₂O₃, and MgO constitutethe core composition. It is also preferred that the glass-ceramicfurther includes at least one of B₂O₃ in an amount up to 10 wt %, P₂O₅in an amount up to 7 wt %, and up to 10 wt % GeO₂. Preferably, thecomposition of the glass-ceramic of the present invention contains 48-57wt % SiO₂, 14-18 wt % Al₂O₃, and 18-25 wt % MgO.

The glass-ceramic according to several embodiments of the presentinvention include cordierite, cristobalite, quartz, or a combination ofthese phases, as a main crystal phase. In some cases, minor crystalphases of cristobalite, quartz, enstatite are also present. It should benoted, however, that when one phase is designated as the main phase, itis not also considered to be a minor phase. In the context of thepresent invention, the phrase “main crystal phase” refers to a crystalphase that is present in an amount that is greater than any other phase.Minor phases are crystal phases that are present in a lesser amount,which is typically less than about 25%. The presence of such main andminor crystal phases is determined by XRD analysis.

The glass-ceramic of the present invention can be provided in a powderor particulate form that can be easily processed. That is, theglass-ceramic can be easily processed into green multi-layer laminatesby mixing the glass-ceramic powders with casting additives and tapecasting the slurry into a green tape that can be made into a pluralityof individual green sheets that can be provided with metallurgy, such asprinted circuitry patterns, and then stacked (layered), laminated andheat-treated at a low temperature to remove organics and the like toform a green multi-layer structure. Other batching and forming methods,including but not limited to roll compaction methods, for example, canalso be used to produce the green multi-layer structure. The greenmulti-layer structure can then be fired at a sintering temperaturebetween 900 and about 1100° C., depending upon the particularcomposition and ultimate application, or alternatively, the greenmulti-layer structure can be prepared and adhered to a support core forco-firing applications.

The glass-ceramic according to the present invention can readily be usedin a wide variety of high frequency electronic applications atfrequencies up to about 60 gigahertz by virtue of the low dielectricconstant and high Q factors. Since the glass-ceramic according to thepresent invention can be thermally processed and compositionallyadjusted to have a desirable TEC range while maintaining the desirablehigh frequency electrical characteristics of a very low dielectricconstant (K) and very high Q, it can be used in connection with avariety of members made of a variety of materials in both co-firing andnon-co-firing applications. It should be noted, however, thatnon-co-firing applications are favored when the glass-ceramic issintered at temperatures exceeding 1000° C. in order to achieve thedesired electrical characteristics.

Examples of such members include metal cores or metal supports made ofKOVAR® or Cu/Mo/Cu, for use in heat sink applications, for example. Theglass-ceramic according to the present invention can also be bonded withactive components, such as certain integrated circuits that are built,for example, on gallium arsenide or silicon bases, as well as othersilicon substrates and gallium arsenide members.

Further, the glass-ceramic according to the present invention is alsocompatible with a variety of thin-film metals, including, but notlimited to, Au, Ag, Al, Ni, Pt, Cu, Pd, Fe, Ti, Cr, and various alloysthereof, and thin-film processing techniques, such as sputtering andCVD, as well as thick-film processing and “personalization processing.”Personalizing the green sheets prior to lamination can involve, forexample, forming vias and filling the vias with suitable via pastes, andforming structural features to define cavities and the like in thefinal, laminated glass-ceramic substrate. Thick-film processingtypically involves printing signal lines, ground planes and the likeusing conductive inks or pastes, for example. Thick-film personalizationinvolving low melting-point metals such as Ag, Au and Cu can be appliedto individual green sheets formed from the compositions according toseveral embodiments of the present invention and co-fired with the greenlaminated structure to relatively low temperatures less than 1050° C.,more preferably, less than 950° C.

In some cases, however, the glass-ceramic of the present invention ismore preferably sintered to temperatures between 1000° C. and 1100° C.Here, a metal or metal alloy having a higher melting-point than Ag (andin some cases, higher melting-point than Au and Cu) would be required inapplications involving applying metallurgy to the green sheets or greenlaminated structure prior to sintering.

According to another embodiment of the present invention, an electronicpackage is provided, including a base member and a glass-ceramicsubstrate bonded to the metal base. The glass-ceramic substrate has athermal expansion coefficient in a range of 3-6 ppm/° C., a dielectricconstant in a range of less than 5 and a Quality factor (1/loss tangent)Q of at least 400. Preferably, the electronic package according to thepresent invention further comprises a bonding layer interposed betweenthe metal base and the glass-ceramic substrate.

According to one embodiment of the present invention, the base member isa metal, such as KOVAR® or laminated Cu/Mo/Cu, and the bonding layer isone of a solder and a bond glass having an appropriately selected, andin this case, relatively low, softening-point, along with an appropriateworking-point and TEC. According to another embodiment of the presentinvention, the base member is a ceramic member, such as a sintered AlNor Al₂O₃ member, and the bonding layer is one of a solder or a bondglass having an appropriately selected softening-point, working-pointand TEC.

When the glass-ceramic substrate is sintered and the base member is ametal, as in some embodiments of the present invention, it is preferredthat the sintered glass-ceramic substrate is metallized before beingbonded with the metal core via a solder. Examples of suitablemetallization are explained in more detail below in connection with theExamples. When the glass-ceramic substrate is green, that is, notsintered, before being bonded with the metal core, metallization is notrequired and the bonding layer is preferably an appropriate bond glass.One of ordinary skill in the art would be readily capable of selectingan appropriate bond glass for such an application, and the choice ofbond glass used in connection with the present invention is not limitedherein.

When the glass-ceramic substrate is sintered and the base member is asintered ceramic, it is preferred that both the glass-ceramic substrateand sintered ceramic base member are metallized before being bonded viaa solder. When a bond glass is used instead of a solder to form thebonding layer between a sintered glass-ceramic substrate and thesintered ceramic base member, metallization of the glass-ceramicsubstrate and sintered ceramic base member is not required, and the bondglass is preferably selected based on appropriate characteristics suchas working-point, softening-point, and TEC. One of ordinary skill in theart would be readily capable of selecting an appropriate bond glass forsuch applications, and the choice of bond glass used in connection withthe present invention is not limited herein. The present invention isnot limited to soldering and bond glass joining methods, and othermaterials such as organic adhesives (e.g., epoxies, organic polymers, ororganic adhesives including ceramic or metallic additives) could also beselected to join the glass-ceramic and the base member when bonding isperformed under the appropriate heat-treatment conditions for theselected bonding material.

Likewise, when the glass-ceramic substrate is green (i.e., not sintered)before being bonded with the sintered ceramic base member, metallizationis not required and the bonding layer is preferably an appropriatelyselected bond glass. Further, in some cases involving green substratesand sintered ceramic cores, an additional bonding agent may not beneeded at all.

The glass-ceramic can also include a conductive pattern, formed incommunication with at least one surface thereof, that is co-fired withthe glass-ceramic substrate (i.e. green sheet or laminated structurepersonalization). Since the glass-ceramic according to some embodimentsof the present invention achieves sufficient densification at low firingtemperatures, conductive patterns and/or metallized regions can beformed on the green laminated body using a relatively low melting-pointmetal, such as Ag.

When a very high Q is desired, however, the glass-ceramic materialaccording to some embodiments of the present invention is preferablysintered to a temperature closer to 1100° C. In this case, a highermelting-point metal would be required for pre-sintering metallization(i.e., personalization) of the glass-ceramic substrate.

The TEC of the glass-ceramic according to the present invention eithermatches or is easily adjusted to achieve a close TEC match with that ofthe support material to which the glass-ceramic substrate is bonded inhigh frequency electronic applications. For example, the α_(RT-300) of anon Ni-plated, laminated Cu/Mo/Cu metal core is about 5.3 ppm/° C., andthe α_(RT-300) of the glass-ceramic material according to one embodimentof the present invention is 5.4 ppm/° C. (see Example 14). The closematch ensures good bonding (e.g., via a solder when the glass-ceramicmaterial is metallized) without thermal mismatch defects such ascracking or bowing at low temperatures.

When the TEC of the glass-ceramic material according to the presentinvention is significantly higher or lower than that of the material towhich it is bonded, the TEC of the glass-ceramic can be easily adjustedby adding a TEC adjusting additive, such as cordierite, cristobalite,trydimite or quartz, to the glass-ceramic powder at the tape slurrypreparation stage before forming the tapes that are laminated togetherto form the glass-ceramic substrate. Other TEC modifying agents, such asthe glass-ceramic compositions shown in Examples 25 and 26, can also beadded as particulates at the tape slurry preparation stage so long asthe material has a crystal phase that has a desirably higher TECcompared to the glass-ceramic, a low K and a high Q, in order to retainthese preferred characteristics in the mixture.

For example, according to one aspect of the present invention, and asshown in Examples 12-19 and 23, the glass-ceramic further includes 1-15wt % of a crystalline silica material such as quartz (as in Examples 13,15, 16, 18, 19 and 23), cristobalite or trydimite or, alternatively,another material that crystallizes to produce these phases, such as thecomposition of Example 25 used in Examples 14 and 17. The additive isprovided as a particulate to the glass-ceramic material during the tapeslurry preparation stage when the TEC of the base member would be higherthan that of the un-modified glass-ceramic substrate. More preferably,4-10 wt % of one of these TEC increasing additives is included. Forexample, certain borosilicate glasses, when prepared in the form of apowder, can also be added in an amount of 1 to 20 wt %, preferably 4-12wt %, at the tape slurry preparation stage to adjust the properties ofthe glass-ceramic of the present invention.

In some cases, it may also be desirable to add a TEC reducing agent tolower the TEC of the glass-ceramic to better match that of a lower TECmember to which it is to be joined, or to positively affect the otherproperties of the glass-ceramic, such as K. In this case, an amount offused silica, for example, preferably 1 to 15 wt %, is added to theglass-ceramic powder at the tape slurry preparation stage. Cordieritecan also be added in an amount of 1 to 15 wt %, preferably 4-10 wt %,although it should be noted that while cordierite can lower the TEC,excessive additions can negatively affect the overall crystal structureof the glass-ceramic resulting in the formation of too much cordieritewhich leads to higher Ks and excessively low TECs.

Similarly, glasses or glass ceramics having a low K, high Q andrelatively low TEC can also be added as particulates at the tape slurrypreparation stage to desirably adjust the characteristics of theglass-ceramic of the present invention. For example, certainborosilicate glasses, when prepared in the form of a powder, can also beadded in an amount of 1 to 20 wt %, preferably 4-12 wt %, at the tapeslurry preparation stage to adjust the properties of the glass-ceramicof the present invention. An example of such a suitable borosilicateglass composition is shown in Example 27.

According to another embodiment of the present invention, a method ofmaking a glass-ceramic substrate having a thermal expansion coefficientin a range of 3-6 ppm/° C., a dielectric constant of less than 5 and aQuality factor Q of at least 400 for use in high frequency electricalapplications is provided. The method includes the steps of providing aglass-ceramic powder having an average particle size in a range of 1-20μm and consisting essentially of SiO₂ in a range of 45-58 wt %, Al₂O₃ ina range of 10-18 wt % and MgO in a range of 10-25 wt %; combining theglass-ceramic powder with processing additives to form a slurry or drymixture; forming a green body from the slurry or dry mixture; sinteringthe green body at a temperature in a range of 900-1150° C. for up to 6hours to form a sintered glass-ceramic body; and cooling the sinteredglass-ceramic body to form the glass-ceramic substrate.

The forming step preferably comprises a method selected from the groupconsisting of a doctor blade method, a roll compaction method, anextrusion method and a dry press method.

Preferably, the green body comprises a plurality of green sheets thatare laminated under heat and pressure to form a laminated greenmulti-layer structure. It is also preferred that at least one of thegreen sheets is metallized, and that the metallized green sheet includesat least one of a structure selected from the group consisting of anelectrode pattern, a conductive via, a cavity and a pattern made of atleast one of a ceramic and a glass.

According to one aspect of the method according to the presentinvention, the sintering step is performed at a temperature of about900° C. for 10 minutes. According to another aspect of the methodaccording to the present invention, the sintering step is performed at atemperature of about 1000° C. for 1 hour. According to yet anotheraspect of the method according to the present invention, the sinteringstep is performed at a temperature of about 1100° C. for 3 hours.

The method according to the present invention can also include the stepsof providing an additive consisting of a particulate material selectedfrom the group consisting of a thermal expansion coefficient increasingadditive and a thermal expansion coefficient reducing additive, theadditive having a particle size in a range of 1-20 μm; and adding theadditive to the glass-ceramic powder in the combining step.

According to one aspect of the method according to the presentinvention, the thermal expansion coefficient increasing additivecomprises 1-15 wt % crystalline silica, which can preferably includes atleast one of 4-10 wt % quartz, 4-10 wt % cristobalite and 4-10 wt %trydimite.

According to another aspect of the method according to the presentinvention, the thermal expansion coefficient increasing additivecomprises 4-12 wt % of a borosilicate glass. According to yet anotheraspect of the method according to the present invention, the thermalexpansion coefficient increasing additive comprises 1-15 wt % of amaterial having a composition consisting essentially of 50-55 wt % SiO₂,12-18 wt % Al₂O₃, 10-18 wt % MgO and 4-16 wt % ZnO and having a primarycrystal phase consisting of crystalline silica.

According to still another aspect of the method according to the presentinvention, the thermal expansion coefficient reducing additive comprisesat least one of 4-12 w % of a borosilicate glass, 1-15 wt % cordieriteand 1-15 wt % fused silica.

It should also be noted that the glass-ceramic according to the presentinvention is a true glass-ceramic material having a crystalline phaseincluding a glassy intergranular phase matrix, not merely aceramic-and-glass composite material made from a mixture of ceramics andglasses, as is the case with many prior art LTCC compositions.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the nature and objects of the presentinvention, reference should be made to the following detaileddescription of a preferred mode of practicing the invention, read inconnection with the accompanying drawings and Examples, in which:

FIG. 1 is a cross-sectional view of a ceramic packaging assemblyaccording to one embodiment of the present invention;

FIG. 2 a is a cross-sectional end view of an intermediate stage inpreparing an a ceramic packaging assembly according to anotherembodiment of the present invention;

FIG. 2 b is a cross-sectional view of the final ceramic packagingassembly of FIG. 2 a;

FIG. 3 is a cross-sectional view of a ceramic packaging assemblyaccording to another embodiment of the present invention;

FIG. 4 a is a cross-sectional end view of an intermediate stage inpreparing an a ceramic packaging assembly according to anotherembodiment of the present invention; and

FIG. 4 b is a cross-sectional view of the final ceramic packagingassembly of FIG. 4 a.

DETAILED DESCRIPTION OF THE INVENTION

The glass-ceramic of the present invention consists essentially of SiO₂in a range of 45-58 wt %, Al₂O₃ in a range of 10-18 wt % and MgO in arange of 10-25 wt %.

When more than about 58 wt % SiO₂ is added, the higher silicaconcentration makes the glass-ceramic difficult to melt, densify, andcrystallize at relatively low temperatures below about 950° C., or evenat temperatures less than 1100° C. When less than about 45 wt % SiO₂ isadded, the lower silica concentrations tend to promote excessively rapidcrystallization, crystallization at relatively low temperatures, reducesthe tendency for stable glass-ceramic formation and tends to promote ahigher TEC, a higher K and a lower Q, which is undesirable.

When more than about 18 wt % Al₂O₃ is added, the higher aluminaconcentration tends to result in more rapid crystallization, a highercordierite level and higher TECs and Ks. When less than about 10 wt %Al₂O₃ is added, the lower alumina concentration levels result in atendency to produce lower glass-ceramic formation and materials thatcrystallize rapidly (which are difficult to process successfully), ahigher K, a higher TEC and a lower Q.

When more than about 25 wt % MgO is added, the higher magnesiaconcentration decreases the stability of glass-ceramic formation and canundesirably increase the crystallization rate, and increase K and theTEC. When less than about 10 wt % MgO is added, the lower magnesiaconcentration can lead to excessively refractory materials with highdensification and crystallization temperatures, or an excessively high Kand low Q, if other fluxing materials are used in addition to MgO.

Oxides of boron (i.e., B₂O₃), phosphorus (i.e., P₂O₅) and germanium(GeO₂) can also be provided as fluxing and glass-forming materials toassist in controlling the melting behavior and reducing the crystalgrowth rate for the glass-ceramic compositions according to the presentinvention. This provides a beneficial increase in the processing range(time-temperature-heating rate) and overall manufacturability of theglass-ceramic according to the present invention. If included, B₂O₃ ispreferably provided in an amount of up to 10 wt %, and more preferablyless than 5 wt %, and P₂O₅ is provided in an amount of up to 10 wt %,preferably less than 7 wt %, and more preferably less than 3 wt %.Similarly, if included, GeO₂ is preferably provided in an amount of upto 10 wt %, and more preferably 5 wt %, to achieve similar results,though GeO₂ tends to be a more expensive component and is thus slightlyless desirable form that standpoint.

When provided in an amount up to 10 wt %, B₂O₃ desirably improvesglass-ceramic formation, the tendency for successful glass melting, andthe promotion of controllable crystallization rates and workablematerials, as well as expands the compositional range forsuitable/workable materials. B₂O₃ concentrations exceeding 10 wt %,however, can result in a higher K, lower Q and higher TEC, generallyinterfere with the development of the preferred crystalline phases, andcan also prevent the use of BUTVAR® as a tape binder, producing anundesirable gelling reaction.

Low levels of phosphorous pentoxide, i.e., to 3-7 wt %, function in amanner similar to the boron oxide in assisting in glass melting andproviding a relatively stable glass-ceramic formation. At concentrationlevels higher than about 7 wt %, however, P₂O₅ tends to enhance thecrystallization tendency and rates and can thus lead to poor controlover devitrification and densification problems.

Germanium oxide additions are functionally analogous to boron oxideadditions. Combinations of boron and germanium oxides or boron,phosphorus and germanium oxides can be very useful in controllingcrystallization kinetics, as shown in the Examples herein.

Although BaO and SrO are not specifically present in the formulationsaccording to the present invention, these materials can be present insmall amounts to adjust the properties. In larger concentrations,however, BaO and SrO tend to produce Ba and Sr aluminosilicate phasesthat have relatively high dielectric constants. The presence of thesecomponents also tends to increase TEC, which in and of itself may notpose a significant problem. Zinc additions, such as ZnO, are also notpresent in the formulations according to the present invention, althoughit is less likely that zinc will result in the development of higher Kphases and can therefore be useful in adjusting the characteristics ofthe glass-ceramic of the present invention.

As explained in more detail below, TEC modifying agents such ascrystalline silica (e.g., quartz, trydimite and cristobalite) can alsobe added to the glass-ceramic composition powders of the presentinvention after at the slurry preparation stage increase the TEC of theglass-ceramic and produce a glass-ceramic substrate that has a TEC thatmore closely matches the TEC of the core or support member to which itis to be bonded. The glass-ceramic substrates of Examples 12-19 and 23include TEC modifying additives that are added as a particulate at thetape slurry preparation stage.

Materials other than quartz and cordierite can also be used as TECmodifying agents to tailor the TEC of the glass-ceramic according to thepresent invention to more closely match that of the base material towhich the glass-ceramic is to be bonded. For example, fused silica has avery low TEC of 0.5 ppm/° C., a low dielectric constant of 3.8 and ahigh Q exceeding 500, and can be favorably used to lower the TEC of theglass-ceramic instead of cordierite. Additionally, while quartz offers avery high TEC of 18 ppm/° C., a low dielectric constant of 4.2 and ahigh Q, other materials can also be used to increase the TEC of theglass-ceramic, such as the glass-ceramic of Examples 25 and 26, which,when processed at high temperatures, have a high TEC, low dielectricconstant and very high Q.

The glass-ceramics according to the present invention are formed in thefollowing manner. Raw materials, including oxides, hydroxides, peroxidesand carbonates of the compositional components of the desiredglass-ceramic composition are mixed (homogenized) and the mixture isplaced in a Pt crucible, for example, which is then heated to atemperature of about 1400-1600° C. The molten glass-ceramic is rapidlycooled or quenched and pulverized into a glass-ceramic powder having anaverage particle size on the order of 1-15 μm. This glass-ceramic powderis suitable for processing green structures, e.g., multi-layer greensheet structures, which can be personalized, laminated, sintered,metallized and bonded to a support member or core at low temperatures(i.e., a non-co-firing application). The laminated green sheetstructures can also be personalized, laminated and simultaneouslysintered with a core material at higher temperatures (i.e., a co-firingsituation).

A green multi-layer laminated structure is formed in the followingmanner. The glass-ceramic powder obtained as described above is combinedwith suitable processing additives, such as binders, solvents,plasticizers, dispersants and viscosity adjusters to produce mixture,such as a tape slurry. Examples of suitable processing additivesinclude, but are not limited to, methyl and ethyl alcohol, toluene,MIBK, MEK (or water), BUTVAR® (polyvinyl butyral), or acrylic binders,dibutyl phathalate and fish oil.

In some instances, it may be desirable to add, for example, an additiveconsisting of 0.5-15 wt % cordierite or fused silica, preferably 2-10 wt% cordierite, as a particulate during the tape slurry preparation stageafter the glass-ceramic is formed and pulverized into a powder butbefore green tapes are formed. This is preferred when the TEC of thebase material to which the glass-ceramic is to be joined is lower thanthat of the glass-ceramic. In this case, for example, in the examplesillustrated herein, that the TEC reducing additive has an averageparticle size of 0.1-20 μm, and in particular, that the added cordieritehas an average particle size of 1 μm.

It should be noted that the particle size and amount of addedcordierite, or another TEC reducing additive, are important when theseadditives are used as nucleating agents. For example, small amounts ofcordierite may also be desired to assist in nucleating or otherwisepromoting a cordierite phase in the glass-ceramic.

Alternatively, it may be desirable to add, for example, additivesconsisting of crystalline silica or a mixture of, for example, ofcrystalline silica and cordierite can be added as particulates duringthe tape slurry preparation stage. More preferably, cordierite is addedin a range of up to 4 wt % and quartz is added in a range of up to 15 wt%. This is preferred when the TEC of the base material to which theglass-ceramic is to be joined is higher than that of the glass-ceramic.In this case, the TEC increasing additives according to the examplesillustrated herein had an average particle size of 0.1-20 μm and inparticular, the added quartz had an average particle size of 3 μm.

It should be noted that the particle size and amount of added quartz oranother additive are important when these materials are used asnucleating agents. For example, small amounts of quartz or cristobalitemay also be desired to assist in nucleating or otherwise promoting acrystalline silica phase in the glass-ceramic.

The tape slurry is tape cast using a doctor blade, for example, or anyother suitable forming method, such as roll compaction, to form one ormore green bodies (e.g., green tapes) having a thickness of about 8-12mm. Green bodies could also be formed by dry pressing if the slurryforming step is omitted and the proper processing additives (i.e., thoseconducive to dry pressing) are added, and by roll compaction orextrusion if a plastic mass is made instead of a slurry by adding theappropriate processing additives to the glass-ceramic powder. The greentapes are cut into individual green sheets about 75 mm long and 75 mmwide, and a number of these green sheets, for example, 6, are stackedtogether to form a multi-layer green sheet structure.

The multi-layer green sheet structure is laminated under heat andpressure conditions. For example, the multi-layer green sheet structureis laminated at a temperature of 50-75° C. and a pressure of 100-500psi, to form a green multi-layer laminated structure.

It should be noted that, prior to lamination, the individual greensheets can also be “personalized,” or provided with a plurality of vias,or other structural features such as cavities, in any conventionalmanner, for example, by punching or milling. Additionally, conductivepatterns can also be provided on the individual green sheets prior tostacking and laminating the multi-layer green sheet structure byprinting or any other suitable method. As mentioned above, since someembodiments of the glass-ceramic of the present invention obtain a highdensity, even when fired at a relatively low firing temperatures ofabout 900° C., low melting-point metals such as Ag paste, for example,which has a relatively low melting-point of 962° C., can be used tometallized the substrate, or to form printed circuits on the individualsheets.

A sintered glass-ceramic substrate that is metallized for ceramicpackaging applications in a non-co-firing situation is formed asfollows. The green multi-layer laminated structure formed as describedabove is heated to a temperature of less than 500° C. to remove bindersand organics in the like at a slow ramp rate of 2-3° C./min forapproximately 10-60 minutes. If conductive pastes to form circuitpatterns are provided prior to lamination by printing, for example, themetal of the conductive paste should be selected depending upon thetemperature at which the green multi-layer laminated structure is to besintered.

For example, in a low temperature application, the green multi-layerlaminated structure is then fired at a faster ramp rate of 5-10° C./minto a temperature of about 900° C. and held for 10-15 minutes to densifyand sinter the green multi-layer laminated structure to form aglass-ceramic substrate and to allow crystalline phases to develop inthe glass-ceramic substrate. In this case, Ag, Cu and Au pastes, orpastes made from alloys of these materials, can be used forpre-sintering personalization.

The green multi-layer laminated structure could instead be fired at afaster ramp rate of 5-10° C./min to a temperature of about 950° C. to1025° C. and held for 10-15 minutes, or up to several hours, ifnecessary or desired, to fully sinter and densify the green multi-layerlaminated structure to form a glass-ceramic substrate and to allow thedesired crystalline phases to develop in the glass-ceramic substrate. Inthis case, Cu and Au pastes, or pates made from alloys of thesematerials or alloys of AgPd and other refractory Ag alloys, can be usedfor pre-sintering personalization. It should be noted, however, thatpure Ag pastes are not utilized when the firing temperatures exceed themelting point of un-alloyed silver.

Furthermore, the green multi-layer laminated structure could instead befired at a faster ramp rate of 5-10° C./min to a temperature of about1100° C. and held for 1-3 hours to sinter and fully densify the greenmulti-layer laminated structure to form a glass-ceramic substrate.Firing at this increased sintering temperature also allows the desiredcrystalline phases, such as cristobalite, quartz and trydimite, tofurther develop in the glass-ceramic substrate to provide an extremelyhigh Q while maintaining the desired K and TEC, or, if desired,increasing the TEC.

It should be noted that adding a nucleating agent such as quartz at thetape slurry preparation stage, as mentioned above, can also be helpfulin this regard with respect to promoting the formation of the desiredcrystalline phases. In this case, a metal having a higher melting-pointthan Ag, and possibly even higher than Au and Cu, should be selected forthe conductive paste if pre-sintering personalization is provided.

In each of the cases mentioned above, after the sintered glass-ceramicsubstrate has cooled, the surfaces may be ground, if necessary, toachieve a desired substrate thickness, preferably 0.15-1 mm forelectronic package applications, for example, and 0.15-4 mm forstand-alone substrate applications, and also to flatten out thesubstrate surfaces. After being ground to the desired thickness andflattened (if necessary), the glass-ceramic substrate is then metallizedin preparation for solder bonding. That is, a thin film metal, such asAu or a sandwich of Ti—Ni—Au or alloys thereof, is applied to thesurfaces of the glass-ceramic substrate by sputtering, for example.

It should be noted that other glass-ceramic substrate preparationoptions include providing a metallization pattern before sintering thegreen multi-layer substrate and omitting the grinding and post-sinteringmetallization step. Further, a green multi-layer laminated structure canbe provided with a thick-film metal, sintered and then ground, ifnecessary, to achieve the desired flatness. If the grinding step isnecessary, a thin film metal can thereafter be applied to the sinteredglass-ceramic substrate. If the grinding step is not necessary, the thinfilm metal can be applied after the sintering step.

The metallized glass-ceramic substrate is then subjected to an etchingprocess, such as photolithography or chemical etching, to form a patternof solder bands. It should be noted that the positions of the solderbands preferably correspond to the outline of the perimeter ofrectangular holes or other similar features that may be provided in themetal cores or sintered ceramic (or other) base members to whichglass-ceramic substrate is bonded. Solder bands can also be formed usinga post-sintering thick film metallization technique, such as printing,for example. In this case, however, photolithography or other etchingprocesses may not be required. In addition, certain hybrid technologies,i.e., a combination of thick and thin-film processes, can be used toprepare the glass-ceramic substrate for solder bonding. For example, athick-film (i.e., screen printed) metal blanket can be provided and thenetched to form solder bands, or even circuit patterns, using thin-filmprocessing techniques.

In cases where the core member is a metal, such as a non-Ni-plated,laminated Cu/Mo/Cu metal core, the metallized glass-ceramic substrate ispositioned over a core member to form an assembly. In cases where thebase member is a sintered ceramic, however, the sintered ceramic basemember is also metallized in preparation for solder bonding, in the samemanner as described above in connection with the metallization of theglass-ceramic, before the metallized glass-ceramic substrate ispositioned over the sintered ceramic base member to form an assembly.

A solder material, such as an Au/Sn solder, is applied to the solderbands. The assembly is heated to a temperature of about 280° C. toreflow the solder and to form a bond between the glass-ceramic substrateand the metal core or sintered ceramic base member. Since the bondingtemperature of the assembly is relatively low, that is, less than 300°C., it is important that the α_(RT-300) values for the glass-ceramicsubstrate and the metal core or sintered ceramic core closely match inthis temperature range.

On the other hand, in co-fired ceramic packaging applications, the greenmulti-layer laminated structure is not sintered prior to being joinedwith the metal core or sintered ceramic base member, and althoughpersonalization metallization may be provided, the bonding surface ofthe green multi-layer laminated structure is not metallized as describedabove for the sintered glass-ceramic that is joined to a base member viasolder. In co-firing applications where the support member is a metalcore, such as a laminated Cu/Mo/Cu core, the surfaces of the Cu/Mo/Cucore may desirably be coated with Ni, for example, by plating. It shouldbe noted, however, that the method for applying the Ni layer to thelaminated Cu/Mo/Cu metal core is not limited to plating, and can also beformed by thin-film techniques, for example. The Ni-coated Cu/Mo/Cu coreis heat-treated to a temperature of about 650-850° C. for 2-20 minutesto oxidize the Ni.

In cases where the base member is a sintered ceramic, however this Niplating may not be necessary in order to provide a suitable bond betweenthe glass-ceramic substrate and the sintered ceramic base member duringheat treatment. Preferably, the bond glass mentioned below should adheredirectly to the sintered ceramic base member without requiring Niplating. It should be noted, however, that the above-described Niplating process could, in fact, be used in connection with a sinteredceramic base member, as well as alternate metallization strategies, ifneeded.

A low softening-point bond glass paste is provided by screen printing,for example, onto the joining surface of the base member. When anoxidized, Ni-plated Cu/Mo/Cu core is used, the core is then heat-treatedat a temperature of about 550-800° C. for 5-30 minutes to burn out thepaste binders and organics and to flow the bond glass particles into asmooth, adherent film. When the support member is a sintered ceramic, ananalogous procedure will produce an analogous structure.

In cases where the support member is a metal core, a binder, preferablythe same binder that was used to form the green tapes (described above),is combined with an organic adhesive, such as MIBK or MEK with alcoholto form an organic adhesive, which is applied to the surface of the bondglass film on the joining surface of the Ni-coated Cu/Mo/Cu core. Thegreen multi-layer laminated structure is positioned on the organicadhesive/glass film-coated surface of the Cu/Mo/Cu core to form anassembly. The assembly is then fired together to a temperature of about900° C. for 10-15 minutes and then cooled. When the support member is asintered ceramic, an analogous procedure will produce an analogousstructure.

In the Examples detailed below, methods of forming the glass-ceramicsaccording to the present invention are described in detail, and thethermal and electrical properties of the glass-ceramics are shown withrespect to the different thermal cycles to which they were subjectedwhen the green multi-layer laminated structures (formed fromglass-ceramic powder as described above) were sintered at varioussintering temperatures ranging from 900 to 1100° C. Suitable examples ofceramic packaging applications and methods of preparing these ceramicpackages are also described in detail.

The thermal cycles are reported in terms of maximum times andtemperatures. Dielectric constant (K) measurements were made using aKent resonant fixture at a frequency of 10-15 gigahertz. Thermalexpansion coefficients (TEC or α) were measured using a commercialpush-rod dilatometer (Theta, Inc.) and, unless otherwise noted,represent the average thermal expansion coefficient from roomtemperature to 300° C. X-Ray Diffraction (XRD) analysis was performed onthe samples using a commercial unit manufactured by Philips and the datawas obtained using MDI Datascan software with Phase ID analysis usingMDI Jade 6.0 software.

It should be understood by those skilled in the art that the presentinvention is in no way limited to the examples described herein, andthat variations and substitutions can be made without departing from thescope and spirit of the present invention.

EXAMPLE 1

A glass-ceramic having the composition shown in Table I was formed bybatching and combining various oxides and carbonates (i.e., raw materialforms) of each of the constituent components in the amounts shown. Theraw material components were mixed (homogenized) and the mixture wasplaced in a Pt crucible, which was heated to a temperature of about1500° C. for about 3 hours. The glass-ceramic was cooled and pulverizedinto a powder having an average particle size on the order of 8 μm.

EXAMPLE 2

A glass-ceramic powder having the composition shown in Table I wasproduced in the same manner as described above in connection withExample 1.

EXAMPLE 3

A glass-ceramic power having the composition shown in Table I wasproduced in the same manner described above in connection with Examples1 and 2.

EXAMPLE 4

A glass-ceramic substrate was formed using the glass-ceramic powder fromExample 1 in the following manner. The glass-ceramic powder of Example 1was combined with an organic binder system including a BUTVAR®-basedbinder, fish oil, and methyl ethyl ketone (MEK), to form a tape slurry.The tape slurry was tape cast using a doctor blade to form green tapeshaving a thickness of about 10 mils (0.254 mm). The green tapes were cutinto individual green sheets about 75 mm long and 75 mm wide, and six ofthese green sheets were stacked together to form a multi-layer greensheet structure. The multi-layer green sheet structure was laminated ata temperature of 85° C. and a pressure of 300 psi, to form a greenmulti-layer laminated structure. The green multi-layer laminatedstructure was slowly heated in a belt furnace at a ramp rate of about2-3° C./min through a temperature range of about 100-400° C. to removethe binder(s), residual solvents and other organics. The ramp rate wasthen increased to 5-10° C./min to a temperature of about 900° C., whichwas held for 10-15 minutes to densify and sinter the green multi-layerlaminated structure into a glass-ceramic substrate and to allow thecrystalline phases to develop in the glass-ceramic substrate.

The characteristics of the glass-ceramic substrate produced according toExample 4 are shown in Table I. In addition, the glass-ceramic ofExample 4 had a main crystal phase of cordierite and also included minorphases of enstatite, crystalline silica, and glass.

EXAMPLE 5

A glass-ceramic substrate was formed using the glass-ceramic powder fromExample 2 in the same manner described above in connection with Example4. In addition to the characteristics of the glass-ceramic substrateproduced according to Example 5 that are shown in Table I, theglass-ceramic of Example 5 had a cordierite main crystal phase and minorphases including a cristobalite phase, a magnesium silicate phase and aglass phase.

EXAMPLE 6

A glass-ceramic substrate was formed using the glass-ceramic powder fromExample 3 in the same manner described above in connection with Example4. The characteristics of the glass-ceramic substrate produced accordingto Example 6 are shown in Table I. In addition, the glass-ceramic ofExample 6 had a main crystal phase of cordierite as well asclinoenstatite and glass phases.

EXAMPLE 7

A glass-ceramic substrate was formed using the glass-ceramic powder fromExample 1 in the same manner described above in connection with Example4, with the exception of the sintering time and temperature. In Example7, the sintering temperature was 950° C. and the hold time was 6 hours.The characteristics of the glass-ceramic substrate produced according toExample 7 are shown in Table I. In addition, the glass-ceramic ofExample 7 had a cordierite main crystal phase and cristobalite and glassphases, as well.

EXAMPLE 8

A glass-ceramic substrate was formed using the glass-ceramic powder fromExample 2 in the same manner described above in connection with Example4, with the exception of the sintering time and temperature. In Example8, the sintering temperature was 950° C. and the hold time was 6 hours.The characteristics of the glass-ceramic substrate produced according toExample 8 are shown in Table I. In addition to the characteristics ofthe glass-ceramic substrate produced according to Example 8 that areshown in Table I, the glass-ceramic of Example 8 had a cordierite maincrystal phase and minor phases including a cristobalite phase, aclinoenstatite phase and a glass phase.

EXAMPLE 9

A glass-ceramic substrate was formed using the glass-ceramic powder fromExample 3 in the same manner described above in connection with Example4, with the exception of the sintering time and temperature. In Example9, the sintering temperature was 950° C. and the hold time was 6 hours.The characteristics of the glass-ceramic substrate produced according toExample 9 are shown in Table I.

EXAMPLE 10

A glass-ceramic substrate was formed using the glass-ceramic powder fromExample 1 in the same manner described above in connection with Example4, with the exception of the sintering time and temperature. In Example10, the sintering temperature was 1100° C. and the hold time was 3hours. The characteristics of the glass-ceramic substrate producedaccording to Example 10 are shown in Table I. In addition to thecharacteristics of the glass-ceramic substrate produced according toExample 10, the glass-ceramic of Example 10 had a cordierite maincrystal phase and minor phases including cristobalite andproto-enstatite.

EXAMPLE 11

A glass-ceramic substrate was formed using the glass-ceramic powder fromExample 1 in the same manner described above in connection with Example4, with the exception of the sintering time and temperature. In Example11, the sintering temperature was 1100° C. and the hold time was 3hours. The characteristics of the glass-ceramic substrate producedaccording to Example 11 are shown in Table I. In addition to thecharacteristics of the glass-ceramic substrate produced according toExample 11, the glass-ceramic of Example 11 had a cordierite maincrystal phase and minor phases including cristobalite, quartz, magnesiumsilicate, and a small glassy phase.

EXAMPLE 12

A glass-ceramic substrate was formed using the glass-ceramic powder fromExample 1 in the same manner described above in connection with Example4, with the exception of the sintering time and temperature. In Example12, the sintering temperature was 1100° C. and the hold time was 3hours. The characteristics of the glass-ceramic substrate producedaccording to Example 12 are shown in Table I. In addition to thecharacteristics of the glass-ceramic substrate produced according toExample 12, the glass-ceramic of Example 12 had a cristobalite maincrystal phase and minor phases of quartz, cordierite, enstatite and asmall amount of a glassy phase.

EXAMPLES 13-19

Table I also shows the composition and properties of the glass-ceramicsof Examples 13-19, which have the same compositions as the glass-ceramicof Examples 1-3 with the exception of the additives noted in Table I andexplained in more detail below. In Examples 13-19, the glass-ceramicpowders were prepared according to Example 4, and green multi-layerlaminated structures were provided according the steps described inExample 4. In Examples 13-19, however, the green multi-layered laminatedstructures were each sintered at a temperature of 1100° C. with a 3 hourhold, as shown in Table I.

EXAMPLE 13

In Example 13, the composition was the same as that of Example 1 andfurther included an additive of 5 wt % quartz having an average particlesize of 3 μm that was added at the tape slurry preparation stage. Thecharacteristics of Example 13 are shown in Table I.

EXAMPLE 14

In Example 14, 8 wt % of a pulverized glass-ceramic material having thecomposition shown in Example 25 and an average particle size of about 8μm was added to the glass-ceramic powder of Example 1 at the tape slurrypreparation stage. The green multi-layered laminated structures weresintered were sintered at a temperature of 1100° C. with a 3 hour hold,as shown in Table I. The characteristics of the glass-ceramic of Example14 are also shown in Table I.

As shown in Example 14, glass-ceramic powders having a composition suchas the ones shown in Examples 25 and 26, for example, can be used as TECmodifying (i.e., increasing) agents as described above instead ofquartz. That is, these compositions can be used as TEC increasingadditives for lower temperature firing glass-ceramics if they are firstfired at 1000° C.-1100° C. to crystallize into the high expansion phasesand are then ground into a powder to be added to the glass-ceramiccomposition at the tape slurry preparation stage, as described above.

EXAMPLE 15

In Example 15, 5 wt % quartz having an average particle size of about 3μm was added to the glass-ceramic powder of Example 2 at the tape slurrypreparation stage. The green multi-layered laminated structures weresintered were sintered at a temperature of 1100° C. with a 3 hour hold,as shown in Table I. The characteristics of the glass-ceramics ofExample 15 are shown in Table II.

EXAMPLE 16

In Example 16, 10 wt % quartz having an average particle size of about 3μm was added to the glass-ceramic powder of Example 2 at the tape slurrypreparation stage. The green multi-layered laminated structures weresintered were sintered at a temperature of 1100° C. with a 3 hour hold,as shown in Table I. The characteristics of the glass-ceramics ofExample 16 are shown in Table I.

EXAMPLE 17

In Example 17, 8 wt % of the composition shown in Example 25 having anaverage particle size of about 8 μm was added to the glass-ceramicpowder of Example 2 at the tape slurry preparation stage. The greenmulti-layered laminated structures were sintered were sintered at atemperature of 1100° C. with a 3 hour hold, as shown in Table I. Thecharacteristics of the glass-ceramics of Example 17 are shown in TableI.

EXAMPLE 18

In Example 18, 5 wt % quartz having an average particle size of about 3μm was added to the glass-ceramic powder of Example 2 at the tape slurrypreparation stage. The green multi-layered laminated structures weresintered were sintered at a temperature of 1100° C. with a 3 hour hold,and the resultant characteristics of the glass-ceramic of Example 18 areshown in Table II.

EXAMPLE 19

In Example 19, 10 wt % quartz having an average particle size of about 3μm was added to the glass-ceramic powder of Example 2 at the tape slurrypreparation stage. The green multi-layered laminated structures weresintered were sintered at a temperature of 1100° C. with a 3 hour hold,as shown in Table I. The characteristics of the glass-ceramic of Example19 are also shown in Table I.

EXAMPLES 20-23

Examples 20-23 have the modified compositions noted in Table I. InExamples 20-23, the glass-ceramic powders were prepared according toExample 4, and green multi-layer laminated structures were providedaccording the steps described in Example 4. In Examples 20-23, however,samples of each of the green multi-layered laminated structures werealso sintered at a temperature of 1000° C. with a 1 hour hold, andsamples of the of the green multi-layered laminated structures Examples20-22 were also sintered to 1100° C. with a 3 hour hold, as shown inTable I.

No TEC adjusting additives were provided at the tape slurry preparationstage in Examples 20-22. Germanium oxide was included in thecompositions of Examples 21 and 22, whereas P₂O₅ was not included in anyof these Examples. B₂O₃ was present in the compositions of Examples 20and 22, either alone or in combination with the GeO₂ as shown in TableI. In Example 23, 5 wt % quartz was added to the composition of Example22.

EXAMPLES 20-23 Sintered at 900 ° C. for 10 Minutes

Table I shows that when the glass-ceramic of 20 was sintered at 900° C.for 10 minutes, the sintered glass-ceramic substrate had K of 5.15 and alow Q of 350. The TEC data for this Example was not obtained since themeasured Q was too low. Similarly, when the glass-ceramic of Example 21was sintered at 900° C. for 10 minutes, the resultant K of 6.0 was toohigh, and the Q of 90 was far too low. The TEC data for this Example wasnot obtained in view of this data. When the glass-ceramic of Example 22was sintered at 900° C. for 10 minutes, the resultant K of 4.95 and Q of440 were better than those of Examples 20 and 21, and the TEC data forthis Example was 5.3 ppm/° C.

EXAMPLES 20-23 Sintered at 1000° C. for 1 Hour

Table 1 shows the results obtained when the samples of theglass-ceramics of Examples 20-23 were sintered at a temperature of 1000°C. for 1 hour. In Example 20, the TEC was measured to be about 4.5 ppm/°C., and the K of 4.8 was lower than that of the Example 20 sample firedat 900° C./10 minutes. Additionally, the Q of Example 20 increased to730 when the green multi-layered laminated structure was sintered at1000° C. for 1 hour.

When the glass-ceramic of Example 21 was sintered at 1000° C. for 1hour, the TEC was measured to be about 6 ppm/° C., and the K of 5.0 waslower than that of the Example 21 sample fired at 900° C./10 minutes.Additionally, the Q of Example 21 increased to 1140 when the greenmulti-layered laminated structure was sintered at 1000° C. for 1 hour.This is a significant increase over the undesirable Q of 90 seen whenthe Example 21 sample was only fired to 900° C./10 minutes. The data isshown in Table I.

When the glass-ceramic of Example 22 was sintered at 1000° C. for 1hour, the TEC was measured to be about 4.5 ppm/° C., and the K of 4.6was lower than that of the Example 22 sample fired at 900° C./10minutes. Additionally, the Q of Example 22 increased to 800. The data isshown in Table I.

When the glass-ceramic of Example 23 was sintered at 1000° C. for 1hour, the TEC was measured to be about 4 ppm/° C., and the K of 4.7 waslower than that of the Example 23 sample fired at 900° C./10 minutes.Additionally, the Q of Example 22 increased to 650. The data is shown inTable I.

EXAMPLES 20-22 Sintered at 1100° C. for 3 Hours

Table I also shows that when the glass-ceramic of Example 20 wassintered at 1100° C. for 3 hours, the sintered glass-ceramic substratehad K of 4.75 and a high Q of 900. In addition, the TEC of theglass-ceramic substrate of Example 20 sintered at 1100° C. for 3 hourswas 3.3 ppm/° C.

When the glass-ceramic of Example 21 was sintered at 1100° C. for 3hours, the sintered glass-ceramic substrate had K of 5.2 and a very highQ of 1240, and a TEC of 5.6 ppm/° C. When the glass-ceramic of Example22 was sintered at 1100° C. for 3 hours, the sintered glass-ceramicsubstrate had K of 4.6 and a high Q of 950, and a TEC of 3.9 ppm/° C.

The marked improvement of K and Q seen when the samples of Examples21-22 were fired at 1100° C. for 3 hours instead of 900° C. for 10minutes is believed to be attributed to the crystal phases thatdeveloped during the longer, hotter sintering period. Thus, in additionto the specific compositions of the present invention, in some cases,the sintering times and temperatures also play a critical role inobtaining the desired TEC, Q and K values.

COMPARATIVE EXAMPLE 24

A glass-ceramic substrate having the composition shown in Table I wasproduced according to the steps outlined in Example 4. XRD analysisindicated that anorthite (CaO—Al₂O₃-2SiO₂) was the primary crystal phasefor this comparative example composition. The high frequency lossproperties of anorthite are known to be inferior to those of the primarycrystal phases present in the above-described glass-ceramic compositionsof Examples 1-3 and 20-22, for example.

As shown in Table I, the glass-ceramic of the Comparative Example 24 hadan extremely low Q value of 135, which is far below the desired Q of atleast 400.

EXAMPLES 25-27

The compositions of the glass-ceramic materials of Examples 25-27 areshown in Table I. The material of Example 25 was formed into aglass-ceramic powder as described above in connection with Example 1.More specifically, the material of Example 25 was heated to temperaturesexceeding 1000° C. during the heat treating step, quenched, ground andthen added to the glass-ceramic of Examples 14 and 17 at the tape slurrypreparation stage, as described in detail above.

The compositions of Examples 25 and 26 can be used as TEC modifyingagents, and also beneficially increase the Q, when the compositions areheat treated to ensure that the resultant powders have the desiredcrystalline phases of cristobalite and/or quartz to adjust the TEC ofthe glass-ceramic compositions to which they are provided as additives.

Example 27 is an example of a borosilicate glass composition that can beadded as a powder to the glass-ceramic composition according to thepresent invention during the tape slurry preparation stage in order toimprove the overall sintering behavior of the glass-ceramic and to helpreduce the K and increase the Q of the resultant glass-ceramic.Additionally, the addition of certain borosilicate glasses aids inobtaining a glass-ceramic that has an increased density.

When borosilicate glasses are chosen as additives, the specific glasscomposition should be selected based on a low K, a high Q, and viscositycharacteristics that allow the glass to have adequate flow properties attemperatures between 800 and 1100° C., but which are suitable rigid attemperatures below 450° C.

In view of the foregoing Examples, it can be taken that he followingmaterials can be suitably fired at temperatures below 950° C. and arethus capable of being co-fired with (pure) silver metallurgy, as well asAu, Cu or alloys of Ag, of Au or of Cu: Example 6; Example 9; Example 22(@900° C./10 min); and Example 23 (@900° C./10 min.). Further, theglass-ceramics of Examples 20-23 are capable of co-firing with Au, Cu oralloys of Au or of Cu at temperatures of about 1000° C. for 1 hour:Example 20 (1000 C./1 hr); Example 21 (@1000 C/1 hr); Example 22 (@1000C/1 hr); and Example 23 (@1000 C/1 hr)

In addition to the information in Table 1, the main and minor crystalphases of some of the Examples are shown below:

-   -   Example 4: Cordierite, enstatite, crystalline silica and glass;    -   Example 7: Cordierite, cristobalite, and a small amount of        glass;    -   Example 10: Cordierite, cristobalite and proto-enstatite;    -   Example 5: Cordierite, cristobalite, magnesium silicate, and low        glass;    -   Example 8: Cordierite, cristobalite, clinoenstatite, and very        low glass;    -   Example 11: Cordierite, cristobalite, quartz, magnesium        silicate, and very low glass;    -   Example 2 plus 10% quartz sintered at 900° C./10 min:        Cordierite, quartz, cristobalite, clinoenstatite, and low glass;    -   Example 16: Cristobalite, cordierite, magnesium silicate, and        very low glass;    -   Example 3: Cordierite, glass and clinoenstatite;    -   Example 12: Cristobalite and quartz, cordierite, enstatite, and        very low glass; and    -   Example 19: Cristobalite and quartz, cordierite, enstatite, and        very low glass.

In the qualitative XRD analysis performed, the presence of glass can beidentified by a broad or diffuse peak of generally lower intensity andoccurring at lower angles, which is distinct from the sharp andfrequently high intensity peaks for dominant crystalline phases.

TABLE I Composition Example 1 Example 2 Example 3 Example 4 Example 5Example 6 Example 7 SiO₂ 54.65 56.60 54.52 Same as Same as Same as Sameas Al₂O₃ 17.50 17.15 17.30 Example 1 Example 2 Example 3 Example 1 MgO24.21 20.34 22.22 P₂O₅ 2.44 2.38 2.40 B₂O₃ 1.20 3.53 3.56 GeO₂ — — — ZnO— — — CaO — — — Additive — — — — — — — Properties:  900° C./10 minα_((RT-300)) 4.5 3.1 3.3 K 5.35 4.77 5.05 Q 350 525 435  950° C./6 hrα_((RT-300)) 4.5 K 5.38 Q 435 1000° C./1 hr α_((RT-300)) K Q 1100° C./3hr α_((RT-300)) K Q Example Example Example Composition Example 8Example 9 10 Example 11 12 13 SiO₂ Same as Same as Same as Same as Sameas Same as Al₂O₃ Example 2 Example 3 Example 1 Example 2 Example 3Example 1 MgO P₂O₅ B₂O₃ GeO₂ ZnO CaO Additive — — — — — 5 wt % QuartzProperties:  900° C./10 min α_((RT-300)) K Q  950° C./6 hr α_((RT-300))2.9 3.6 K 4.75 5.02 Q 5.18 435 1000° C./1 hr α_((RT-300)) K Q 1100° C./3hr α_((RT-300)) 4.6 4.1 5.3 5.2 K 4.85 4.31 4.88 4.8 Q 1150 480 683 1125Example Example Example Example Example Example Example Composition 1415 16 17 18 19 20 SiO₂ Same as Same as Same as Same as Same as Same as55.20 Al₂O₃ Example 1 Example 2 Example 2 Example 2 Example 3 Example 317.51 MgO 22.49 P₂O₅ — B₂O₃ 4.80 GeO₂ — ZnO — CaO — Na₂O — K₂O — Li₂O —Additive 8 wt % 5 wt % 10 wt % 8 wt % 5 wt % 10 wt % — Example QuartzQuartz Example Quartz Quartz 25 25 Properties:  900° C./10 minα_((RT-300)) — K 5.15 Q 350  950° C./6 hr α_((RT-300)) K Q 1000° C./1 hrα_((RT-300)) 4.5 K 4.8 Q 730 1100° C./3 hr α_((RT-300)) 5.4 5.8 7.6 4.97.4 — 3.3 K 4.5 4.5 4.0 4.8 4.3 4.5 4.75 Q 975 650 470 600 530 400 900Comparative Example Example Example Example Example Example ExampleComposition 21 22 23 24 25 26 27 SiO₂ 53.91 49.55 Same as 52.98 53.8153.39 72.0 Al₂O₃ 17.10 16.99 Example 16.96 15.74 14.00 1.0 MgO 21.9721.82 22 15.64 12.45 16.28 — P₂O₅ — — 2.36 2.19 4.59 — B₂O₃ — 4.67 1.173.24 4.51 25.0 GeO₂ 7.02 6.97 — — — — ZnO — — — 12.57 7.23 — CaO — —10.89 — — — Na₂O — — — — — 0.5 K₂O — — — — — 1.0 Li₂O — — — — — 0.5Additive — — 5 wt % — — — Quartz Properties:  900° C./10 minα_((RT-300)) — 5.3 <5 4.8 3.2 K 6.0 4.95 4.85 6.52 — Q 90 440 400 135 — 950° C./6 hr α_((RT-300)) K Q 1000° C./1 hr α_((RT-300)) ~6 4.5 ~4 K5.0 4.6 4.7 Q 1140 800 650 1100° C./3 hr α_((RT-300)) 5.6 3.9 22 K 5.24.6 — Q 1240 950 —

Ceramic Packaging Assembly Examples EXAMPLE 28 Non-Co-Fired CeramicPackaging Assembly with Metal Base Member

A non-co-fired ceramic packaging assembly is formed in the followingmanner. The glass-ceramic substrate of Example 13 is prepared asdescribed above. After the glass-ceramic substrate is ground to thedesired thickness and flattened, a thin film metal of Ti—Ni—Au isapplied to the surfaces of the sintered glass-ceramic substrate bysputtering.

A dry photo resist is laminated to the metallized substrate, exposed anddeveloped under standard processing procedures to provide a protectivemask over the metal. The exposed portions of the metal are removed usingcommercial etchants and procedures, and the photo resist is etched awayto form a pattern of discrete solder bands on the substrate. A soldermaterial comprising an 80/20 Au/Sn eutectic mixture is applied to thesolder bands as a screened paste, and the metallized glass-ceramicsubstrate is positioned over a KOVAR® metal core that is either oxidizedaccording to standard industry practices or plated with a thin layer ofNi and Au to prevent Cu oxidation and to provide a clean surface for thesolder band. It should be noted that, in this case, the metal core isplated with a very thin layer of Ni, having a thickness on the order of1.3 μm, and then a very thin layer of Au, having a thickness on theorder of 0.13 μm, is applied by immersion on both sides. Since the Niand Au layers are very thin, these layers have little to no impact onthe TEC of the metal core.

In cases where a bond glass is used to bond the glass-ceramic substrateand a metal core, however, the metal core is either oxidized by standardindustry procedures or plated with a thicker layer of Ni and oxidized,which does affect the TEC of the core. The assembly is heated to atemperature of 280° C. to reflow the solder and to form a bond betweenthe glass-ceramic substrate and the metal core.

EXAMPLE 29 Non-Co-Fired Ceramic Packaging Assembly with Sintered CeramicBase Member

The glass-ceramic substrate of Example 10 or 11 is prepared as describedabove. The glass-ceramic substrate is then ground to the desiredthickness and flattened, and a thin film metal of Ti—Ni—Au is applied tothe surfaces of the sintered glass-ceramic substrate by sputtering. Adry photo resist is laminated to the metallized substrate, exposed anddeveloped under standard processing procedures to provide a protectivemask over the metal. The exposed portions of the metal are removed usingcommercial etchants and procedures, and the photo resist is etched awayto form a pattern of discrete solder bands on the substrate. A soldermaterial comprising an 80/20 Au/Sn eutectic mixture is applied to thesolder bands as a screened paste, and the metallized glass-ceramicsubstrate is positioned over a sintered ceramic base member made of AlN,having a TEC of 4.5 ppm/° C., which is also metallized in the samemanner as the glass-ceramic substrate. The assembly is heated to atemperature of 280° C. to reflow the solder and to form a bond betweenthe glass-ceramic substrate and the metal core.

EXAMPLE 30 Co-Fired Ceramic Packaging Assembly with Metal Base Member

A co-fired ceramic packaging assembly is produced in the followingmanner. A glass-ceramic powder having the composition of Example 22, or,alternatively, Example 23, is used to produce a green multi-layerlaminated structure as described in Example 4. The Example 22composition is compatible with thick film Ag, Au or Cu (or alloys)patterning. Unlike the metallized glass-ceramic substrate of Example 28,however, the green multi-layer laminated structure of Example 30 is notsintered or metallized for soldering prior to being joined with themetal core.

A KOVAR® core as in Example 28 is provided as a metal core member. InExample 30, however, the surfaces of the KOVAR® core are coated with Niby plating. The KOVAR® core is heat-treated to a temperature of 800° C.for 30 minutes to oxidize the Ni.

A low softening-point bond glass paste having a green thickness of about0.5-2 mils is screen printed onto the joining surface of the KOVAR®core, and heat-treated at a temperature of about 800° C. for 30 minutesto burn out the paste binders and organics and to flow the bond glassparticles into a smooth, adherent film about 0.2-1.5 mils thick.

The same binder used to form the green tapes (described above inconnection with Example 4) i.e., polyvinyl butyral, is combined with amethanol/MEK solvent, and the resultant organic adhesive is applied tothe surface of the bond glass layer to form a film less than 1 mil thickon the joining surface of the KOVAR® core. The thickness of the organicadhesive film is not critical so long as it is sufficient to compensatefor differences in the surface structures of the multi-layer laminatedstructure and the bond glass-coated core.

The green multi-layer laminated structure is positioned on the organicadhesive/glass film-coated surface of the core, and laminated/adhered tothe core to form an assembly. The assembly is then simultaneously firedto a temperature of between 900° C. and 950° C. and cooled.

It should be noted that the Example 20 and Example 21 compositions canalso be processed with the other core materials mentioned above inconnection with Example 30 and laminated Cu/Mo/Cu core materials inco-firing situations, as well as with thick film Au or Cu or alloys, atsomewhat higher temperatures near 1000° C. These applications would,however, require bond glasses having somewhat higher softening-pointsthan those used in the lower firing temperature Examples. One skilled inthe art would not have any difficulty in establishing which glassesmight be appropriately as the bond glasses in these cases.

EXAMPLE 31 Co-Fired Ceramic Packaging Assembly with Sintered CeramicBase Member

A co-fired ceramic packaging assembly is produced in the followingmanner. A glass-ceramic powder having the composition of Example 20 isused to produce a green multi-layer laminated structure as described inExample 4. Unlike the metallized glass-ceramic substrate of Examples 28and 29, however, the green multi-layer laminated structure of Example 31is not sintered or metallized for soldering prior to being joined withthe metal core.

A sintered ceramic base member made of AlN is provided. A bond glasshaving a softening-point in a range of 700-900° C. and a working pointin a range of 850-1050° C. is formed into a paste having a greenthickness of about 0.5-2 mils that is screen printed onto the joiningsurface of the AlN core, and heat-treated at a temperature of about 900°C. for 30 minutes to burn out the paste binders and organics and to flowthe bond glass particles into a smooth, adherent film about 0.2-1.5 milsthick.

The same binder used to form the green tapes (described above inconnection with Example 4) i.e., polyvinyl butyral, is combined with amethanol/MEK solvent, and the resultant organic adhesive is applied tothe surface of the bond glass layer to form a film less than 1 mil thickon the joining surface of the AlN core. The thickness of the organicadhesive film is not critical so long as it is sufficient to compensatefor differences in the surface structures of the multi-layer laminatedstructure and the bond glass-coated core.

The green multi-layer laminated structure is positioned on the organicadhesive/glass film-coated surface of the core, and laminated/adhered tothe core to form an assembly. The assembly is then simultaneously firedto a temperature of about 1000° C. for 1 hour and cooled.

If, on the other had, a ceramic packaging assembly is made using ansintered Al₂O₃ base member instead of a sintered AlN base member, anappropriately selected bond glass would preferably have asoftening-point in a range of 700-950° C. and a working point in a rangeof 850-1100° C. In this case, the bond glass is formed into a pastehaving a green thickness of about 0.5-2 mils that is screen printed ontothe joining surface of the Al₂O₃ core, and heat-treated at a temperatureof about 950° C.-1000° C. for 30 minutes to burn out the paste bindersand organics and to flow the bond glass particles into a smooth,adherent film about 0.2-1.5 mils thick. After the organic adhesive isapplied, the green multi-layer laminated structure is positioned on theorganic adhesive/glass film-coated surface of the glassed Al₂O₃ core,and laminated/adhered to the Al₂O₃ core to form an assembly. Theassembly is then simultaneously fired to a temperature of about 1100° C.for 0.5 to 3 hours and cooled.

FIG. 1 is a cross-sectional view of a ceramic packaging assembly 1according to one embodiment of the present invention, specifically, ametallized multi-layer glass-ceramic substrate 10 that is solder bondedto a metal core 2. The ceramic packaging assembly 1 of FIG. 1 includes aglass-ceramic substrate 10, a metal core 2, and a bonding layer 3disposed between the glass-ceramic substrate 10 and the metal core 2.The ceramic packaging assembly of FIG. 1 can be produced according toExamples 4 as described above, wherein a green multi-layer laminatedstructure (not shown in FIG. 1) having the composition of composition ofExample 22 is sintered to 900° C. for 10 minutes to achieve sufficientdensification of the laminated glass-ceramic green sheet layers toproduce the glass-ceramic substrate 10 having the desired Q, K and TECcharacteristics.

The glass-ceramic substrate 10 is then metallized and etched to definesolder bands at least on the joining surface 10 a thereof, as describedin Example 28. An Au/Sn solder is provided on the solder bands, and thejoining surface 10 a of the glass-ceramic substrate is brought intocontact with the joining surface 2 a of the laminated Cu/Mo/Cu metalcore 2. The assembly is then heated to a temperature of about 280° C. toreflow the solder and define the bonding layer 3, which joins theglass-ceramic substrate 10 and the metal core 2 at the interface betweenthe respective joining surfaces 10 a and 2 a thereof to form the ceramicpackaging assembly 1.

FIG. 2 a is a cross-sectional view of an intermediate step in producinga ceramic packaging assembly 100 according to another embodiment of thepresent invention, specifically involving an un-metallized, greenmulti-layer laminated structure 11 that is bonded to a Ni-plated metalcore 2 via a bond glass layer 30, as described above in Example 30. FIG.2 b is a cross-sectional end view of the final ceramic packagingassembly 100 of FIG. 2 a.

As described above in connection with the Examples, after theglass-ceramic powder of Example 22 is prepared. A tape slurry is formed,and a plurality of green sheets are formed as described above inconnection with Example 30. The green sheets 11 ₁ . . . 11 _(n) are cut,stacked, and laminated to form the green multi-layer laminated structure11 of FIG. 2 a in the manner described in Example 4.

As described in more detail above, and particularly in connectionExample 30, the laminated Cu/Mo/Cu core 2 is plated with Ni, oxidized,and a layer of bond glass paste is printed, or otherwise suitablyprovided, on the joining surface 2 a thereof. The bond glass paste isheated to remove organic constituents and to flow into a smooth,adherent bond glass film on the joining surface 2 a of the Ni-platedmetal core 2. An organic adhesive, such as that described in Example 30,is applied to the bond glass film, and the green laminated structure 11is disposed so that the joining surface 11 a contacts the organicadhesive/bond glass layers on the joining surface 2 a of the Ni-coatedCu/Mo/Cu core 2.

The assembly is then heated to a temperature of about 900° C. for 10minutes to densify the glass-ceramic layers of the green multi-layerlaminated structure 11 into the glass-ceramic substrate 110 of FIG. 2 band to allow the bond glass layer 30 to react with and bond to theglass-ceramic substrate 110 and the metal core 2 as described above. Theglass-ceramic substrate 110 is thus firmly bonded to the Ni-plated,laminated Cu/Mo/Cu core 2 via a bond glass layer 30 interposed betweenthe respective joining surfaces 110 a and 2 a of the glass-ceramicsubstrate 110 and the metal core 2 to form the ceramic packagingassembly 100.

FIG. 3 is a cross-sectional view of a ceramic packaging assembly 100′according to one embodiment of the present invention, specifically, ametallized multi-layer glass-ceramic substrate 101 that is solder bondedto an AlN base member 200 via a bonding layer 300 that is disposedbetween the glass-ceramic substrate 101 and the AlN base member 200. Theceramic packaging assembly of FIG. 3 can be produced according toExample 4 as described above, wherein a green multi-layer laminatedstructure (not shown in FIG. 3) having the composition of Example 22 issintered to 1000° C. for 1 hour to achieve sufficient densification ofthe laminated glass-ceramic green sheet layers to produce theglass-ceramic substrate 101 having the desired Q, K and TECcharacteristics.

The glass-ceramic substrate 101 is then metallized and etched to definesolder bands at least on the joining surface 110 a thereof, as describedin Example 29. An Au/Sn solder is provided on the solder bands, and thejoining surface 110 a of the glass-ceramic substrate is brought intocontact with the joining surface 200 a of AlN base member 200. Theassembly is then heated to a temperature of about 280° C. to reflow thesolder and define the bonding layer 300, which joins the glass-ceramicsubstrate 101 and the AlN base member 200 at the interface between therespective joining surfaces 110 a and 200 a thereof to form the ceramicpackaging assembly 100′.

FIG. 4 a is a cross-sectional view of an intermediate step in producinga ceramic packaging assembly 100″ according to another embodiment of thepresent invention, specifically involving an un-metallized, greenmulti-layer laminated structure 111 that is bonded to a sintered ceramiccore 220 via a bond glass layer 310, as described above in Example 31.FIG. 4 b is a cross-sectional end view of the final ceramic packagingassembly 100″ of FIG. 4 a.

As described above in connection with the Examples, after theglass-ceramic powder of Example 22 is prepared. A tape slurry is formed,and a plurality of green sheets are formed as described above inconnection with Example 4. The green sheets 11 ₁ . . . 11 _(n) are cut,stacked, and laminated to form the green multi-layer laminated structure111 of FIG. 4 a in the manner described in Example 4.

As described in more detail above, and particularly in connectionExample 31, the sintered ceramic core 220 is provided and a layer ofbond glass paste is printed, or otherwise suitably provided, on thejoining surface 220 a thereof. The bond glass paste is heated to removeorganic constituents and to flow into a smooth, adherent bond glass filmon the joining surface 220 a of the AlN core 220. An organic adhesive,such as that described in Example 31, is applied to the bond glass film,and the green laminated structure 111 is disposed so that the joiningsurface 111 a thereof contacts the organic adhesive/bond glass layers onthe joining surface 220 a of the AlN base member 220.

The assembly is then heated to a temperature of about 1000° C. for about60 minutes to densify the glass-ceramic layers of the green multi-layerlaminated structure 111 into the glass-ceramic substrate 112 of FIG. 4and to allow the bond glass layer 310 to react with and bond to theglass-ceramic substrate 112 and the core 220 as described above. Theglass-ceramic substrate 112 is thus firmly bonded to the AlN base member220 via a bond glass layer 310 interposed between the respective joiningsurfaces 112 a and 220 a of the glass-ceramic substrate 112 and the basemember 220 to form the ceramic packaging assembly 100″.

While the present invention has been particularly shown and describedwith reference to the preferred mode as illustrated in the Examples anddrawings, it will be understood by one skilled in the art that variouschanges in detail may be effected therein without departing from thespirit and scope of the invention as defined by the claims.

1. A method of making a glass-ceramic substrate having a thermalexpansion coefficient in a range of 3-6 ppm/° C., a dielectric constantof less than 5 and a Quality factor (Q) of at least 400 for use in highfrequency electrical applications, said method comprising the steps of:providing a glass-ceramic powder having an average particle size in arange of 1-20 μm and consisting essentially of SiO₂ in a range of 45-58wt %, Al₂O₃ in a range of 10-18 wt % and MgO in a range of 10-25 wt %;combining said glass-ceramic powder with processing additives to form amixture; forming a green body from said mixture; sintering said greenbody at a temperature in a range of 900-1150° C. for up to 6 hours toform a sintered glass-ceramic body; and cooling said sinteredglass-ceramic body to form said glass-ceramic substrate.
 2. The methodof claim 1, wherein said green body comprises a green sheet.
 3. Themethod of claim 2, further comprising the steps of providing a pluralityof said green sheets and laminating said plurality of green sheets underheat and pressure to form a laminated green multi-layer structure. 4.The method of claim 1, wherein said sintering step is performed at atemperature of about 900° C. for 10 minutes.
 5. The method of claim 1,wherein said sintering step is performed at a temperature of about 1000°C. for 1 hour.
 6. The method of claim 1, wherein said sintering step isperformed at a temperature of about 1100° C. for 3 hours.
 7. The methodof claim 1, further comprising the steps of: providing an additiveconsisting of a particulate material selected from the group consistingof a thermal expansion coefficient increasing additive, a thermalexpansion coefficient reducing additive, and a sintering aid, saidadditive having a particle size in a range of 1-20 μm; and adding saidadditive to said glass-ceramic powder in said combining step.
 8. Themethod of claim 7, wherein said thermal expansion coefficient increasingadditive comprises 1-15 wt % crystalline silica.
 9. The method of claim7, wherein said additive comprises 4-12 wt % of a borosilicate glass.10. The method of claim 7, wherein said thermal expansion coefficientincreasing additive comprises 1-15 wt % of a material having acomposition consisting essentially of 50-55 wt % SiO₂, 12-18 wt % Al₂O₃,10-18 wt % MgO and 4-16 wt % ZnO and having a primary crystal phaseconsisting of crystalline silica.